I also like to experiment with new 243 loads. The one I currently like best is a 75 Vmax under 38.3 grains of IMR 4064. I'm not sure of velocity, but I do know its not going to be in the 3500 fps range. I load just a touch off the rifiling, and this is my currentl go-to load. I did try 70gr blitzkings, but I could not get them to shoot as well as the hornadys.
Try the 65 grain Vmax. I do know that you can push that up to 3500 plus. Whatever you do, let us know...we all like to hear about what others are up to. Good luck, have fun, and be safe!